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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
12 October 2011 - 23 March 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study was conducted in accordance with International guidelines and GLP. All guideline validity criteria were met.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
17 July 1992
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
Commission Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH).
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
RADIOLABELLING INFORMATION (if applicable)
- Radiochemical purity: N/A
- Specific activity: N/A
- Locations of the label: N/A
- Expiration date of radiochemical substance: N/A

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature, in the dark and under nitrogen.
- Stability under test conditions: Assumed stable.
- Solubility and stability of the test substance in the solvent/vehicle: N/A, applied as supplied
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: N/A

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: N/A, applied as supplied.
- Preliminary purification step (if any): N/A
- Final dilution of a dissolved solid, stock liquid or gel: N/A
- Final preparation of a solid: N/A

FORM AS APPLIED IN THE TEST (if different from that of starting material): Applied as supplied.

TYPE OF BIOCIDE/PESTICIDE FORMULATION (if applicable): N/A

OTHER SPECIFICS: No
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Worlingworth sewage treatment works (Suffolk, UK)
- Preparation of inoculum for exposure: Aerated and solid content determined. The inoculum was added to bottles three days before test initiation to allow a period of ageing.
- Pretreatment: No
- Concentration of sludge: Nominal 30 mg/L in the treatment flasks.
- Water filtered: No
- Type and size of filter used, if any: N/A
Duration of test (contact time):
28 d
Initial conc.:
21.6 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: The mineral salts medium (MSM) for the test was prepared by establishing 10 mL of stock solution 1 and 1 mL of solutions 2, 3 and 4 in each litre of water required for the test.
Stock 1 - Potassium dihydrogen phosphate (8.50 g/L); di-Potassium hydrogen phosphate (21.75 g/L); di-Sodium monohydrogen phosphate dihydrate (33.40 g/L); Ammonium chloride (0.5 g/L)
Stock 2 - Magnesium sulphate heptahydrate (22.50 g/L)
Stock 3 - Calcium chloride dihydrate (36.40 g/L)
Stock 4 - Iron (III) chloride hexahydrate (0.25 g/L)
- Additional substrate: N/A
- Solubilising agent (type and concentration if used): N/A
- Test temperature: 22 ± 2 ºC
- pH: 7.5
- pH adjusted: yes, with 5 M HCl
- CEC (meq/100 g): Not reported
- Aeration of dilution water: Not reported
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes
- Other: N/A

TEST SYSTEM
- Culturing apparatus: 500 mL amber glass culture bottles
- Number of culture flasks/concentration: Blank control = 2; Reference control = 1; Test vessel = 2; Toxicity control = 1
- Measuring equipment: Each bottle was fitted with an electrolytic cell assembly (containing the electrolyte, 1M copper sulfate solution, and the CO2 absorber, 5 mL of 2M potassium hydroxide) and connected to the respirometer (Co-ordinated Environmental Services (CES) Ltd automated respirometer)
- Test performed in closed vessels due to significant volatility of test substance: Yes
- Test performed in open system: No
- Details of trap for CO2 and volatile organics if used: 2 M KOH
- Other: N/A

SAMPLING
- Sampling frequency: Hourly
- Sampling method: Respirometer electronically captured data on an hourly basis.
- Sterility check if applicable: N/A
- Sample storage before analysis: N/A
- Other: N/A

CONTROL AND BLANK SYSTEM
- Inoculum blank: Inoculated MSM only
- Reference control: Inoculated MSM and sodium benzoate (25 mgO2/500 mL)
- Toxicity control: Reaction product of 3,5,5-trimethyl-hexanoic acid and 2-metheylpropanoic acid and pentaerythritol (25 mgO2/500 mL) + sodium benzoate (25 mgO2/500 mL) in inoculated MSM
- Other: N/A

STATISTICAL METHODS: N/A
Reference substance:
other: sodium benzoate
Test performance:
The results obtained for the rate of degradation of sodium benzoate (62 % of its ThOD after 3 days) and for the cumulative amount of oxygen consumed by the control mixtures (29.56 and 22.02 mg O2/L) fulfilled the validity criteria for this test.

In the presence of Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid, the degradation of sodium benzoate achieved 67 % after 3 days indicating that the test substance was not inhibitory to the microbial inoculum.
Key result
Parameter:
% degradation (O2 consumption)
Value:
25
Sampling time:
28 d
Details on results:
Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was not considered to be readily biodegradable under the conditions of this test.
Results with reference substance:
The results obtained for the rate of degradation of sodium benzoate (62 % of its ThOD after 3 days) and for the cumulative amount of oxygen consumed by the control mixtures (29.56 and 22.02 mg O2/L) fulfilled the validity criteria for this test.

Table 1       Respirometry test results

Day

% Biodegradation

Test Item

(50 mgO2/L)

Sodium benzoate

(50 mgO2/L)

Sodium benzoate + Test Item

(50 mgO2/L)

Test 1

Test 2

Mean

1

1

1

1

37

45

2

1

2

2

55

56

3

2

2

2

62

67

4

3

4

3

67

-

5

4

6

5

71

-

6

4

6

5

73

-

7

5

7

6

75

-

8

6

8

7

76

-

9

7

9

8

78

-

10

7

11

9

79

-

11

8

12

10

80

-

12

9

13

11

82

-

13

9

14

11

83

-

14

10

15

13

84

-

15

11

17

14

85

-

16

11

18

15

86

-

17

12

19

16

88

-

18

12

20

16

89

-

19

13

21

17

89

-

20

14

24

19

91

-

21

15

26

20

92

-

22

15

27

21

93

-

23

16

28

22

93

-

24

18

29

23

94

-

25

18

30

24

94

-

26

19

30

25

95

-

27

20

31

26

95

-

28

19

31

25

95

-

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was not considered to be readily biodegradable under the conditions of this test.
Executive summary:

OECD 301F (2012) - The ready biodegradability of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was assessed in accordance with Directive (EC) 440/2008, C.4-D, ‘Determination of Ready Biodegradability, Manometric respirometry’ and OECD Procedure 301F ‘Ready Biodegradability, Manometric Respirometry Test’, adopted 17 July 1992.

 

Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was added to two bottles containing mineral salts medium inoculated with activated sludge (30 mg solids/L) to give a nominal test concentration of 50 mg O2/L. Two control cultures contained inoculated mineral salts medium alone. Two cultures contained inoculated mineral salts medium plus the reference substance sodium benzoate (50 mg O2/L) of which one also contained Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid (50 mg O2/L) in order to assess the potential inhibitory effects of the test substance on the microbial inoculum. The test system comprised of an automated system for oxygen (O2) generation and the cultures were stirred and held in a thermostatically-controlled water bath.

 

The blank-corrected oxygen demanded by the culture containing the reference substance had achieved 15.44 mg O2/500 mL or 62% of the ThOD (25 mg O2/500 mL) after 3 days of incubation.

 

In the presence of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid, degradation of sodium benzoate had achieved 67 % by Day 3. Cumulative levels of oxygen consumption by the controls after 28 days (14.78 and 11.01 mg O2/500 mL, equivalent to 29.56 and 22.02 mg O2/L) were considered to be acceptable for this assay system. These results confirm that Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was not inhibitory to the activity of the microbial inoculum and that the test was valid.

 

Mean oxygen consumption in mixtures containing Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was equivalent to 10 % of the theoretical value (25 mg O2/500 mL) after approximately 11 days and 25 % at the end of the test (Day 28), therefore, Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was not considered to be readily biodegradable under the conditions of this test.

Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
11 May 2012 - 20 December 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study conducted in accordance with International guidelines and GLP. All guideline validity criteria were met.
Qualifier:
according to guideline
Guideline:
OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))
Version / remarks:
12 May 1981
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
RADIOLABELLING INFORMATION (if applicable)
- Radiochemical purity: N/A
- Specific activity: N/A
- Locations of the label: N/A
- Expiration date of radiochemical substance: N/A

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature, in the dark and under nitrogen.
- Stability under test conditions: Assumed stable.
- Solubility and stability of the test substance in the solvent/vehicle: N/A, applied as supplied
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: N/A

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: N/A, applied as supplied.
- Preliminary purification step (if any): N/A
- Final dilution of a dissolved solid, stock liquid or gel: N/A
- Final preparation of a solid: N/A

FORM AS APPLIED IN THE TEST (if different from that of starting material): Applied as supplied.

TYPE OF BIOCIDE/PESTICIDE FORMULATION (if applicable): N/A

OTHER SPECIFICS: No
Oxygen conditions:
aerobic
Inoculum or test system:
mixture of sewage, soil and natural water
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): From sites such as sewage treatment works, industrial waste-water treatment works, rivers, lakes, seas, 1 L samples of sludge, surface soil, water, etc. were collected and mixed thoroughly together.

- Preparation of inoculum for exposure: After removing floating matter and allowing to stand, the supernatant was adjusted to pH = 7.0 ± 1.0 with sodium hydroxide or phosphoric acid. An appropriate volume of the filtered supernatant was filled in a vessel and the liquid was aerated for about 23.5 h. 30 min after stopping aeration, about one third of the whole volume of supernatant was discarded and an equal volume of a solution (pH = 7.0) containing 0.1 % each of glucose, peptone and potassium orthophosphate was added to the settled material and aeration re-commenced. This procedure was repeated once per day. The unit should be operated according to good practice. Test temperature was kept at 25 °C ± 2 °C and at pH = 7.0 ± 1.0; the final obtained sludge should settle well; there was sufficient aeration to keep the sludge aerobic at all times. The sludge can be used as inoculum after at least one month of preparation for not more than three months. Sludge was taken for use as inoculum of the study 18 h-24 h after the unit has been fed.

- Concentration of sludge: The concentration of the inoculum was determinated as 3.2g/L, 469 mL this inoculum was centrifuged (1100 g, 10 min) and the supernatant liquid phase was decanted. Sludge was resuspended in mineral medium to 300 mL to obtain a concentration equivalent to 5.0 g dry material per liter.
Duration of test (contact time):
28 d
Initial conc.:
32 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: The following stock solutions using analytical grade reagents.

Stock solution (a) = Potassium dihydrogen phosphate KH2PO4 (1.7 g), Dipotassium hydrogen phosphate trihydrate K2HPO4·3H2O (5.698 g), Disodium hydrogen phosphate Na2HPO4 (3.54 g), Ammonium chloride NH4Cl (0.34 g) (Dissolved in water and made up to 200 mL and adjusted to pH 7.2)

Stock solution (b) = Anhydrous calcium chloride CaCl2 (13.75 g) (Dissolved in water and made up to 500 mL).

Stock solution (c) = Magnesium sulfate heptahydrate mgSO4·7H2O (11.25 g) (Dissolved in water and made up to 500 mL)

Stock solution (d) = Iron (III) chloride hexahydrate FeCl3·6H2O (0.125 g) (Dissolved in water and made up to 500 mL)

30 mL of solution (a), (b), (c) and (d) was mixed and made up to 10 L with water.

- Test temperature: 25 ± 1 ºC
- pH: 7
- pH adjusted: yes
- Aeration of dilution water: No
- Suspended solids concentration: 5 g/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: Culture bottles with air-tight seals connected to a Bioscience Inc. BI-2000 respirometer.
- Number of culture flasks/concentration: Abiotic control = 1 (Bottle 1); Test vessels = 3 (Bottles 2-4); Procedure control = 1 (Bottle 5); Inoculum blank = 1 (Bottle 6) and Toxicity control = 1 (Bottle 7).
- Measuring equipment: Bioscience Inc. BI-2000 respirometer
- Test performed in closed vessels due to significant volatility of test substance: Yes
- Test performed in open system: No

SAMPLING
- Sampling frequency: Respirometer recorded uptake of O2 hourly. The residual amount of the test substance in bottles 1, 2, 3 and 4 was determined at the end of the test.
- Sampling method: The thermometer recorded temperature of water bath automatically once an hour during the experiment period. The electrolyte solution, stirrer and any changes in colour of the contents in vessels on a daily basis. The respirometer recorded the oxygen uptake of each test vessel automatically once an hour during the experiment period. Determined the pH of each bottle at the end of the test. The residual amount of the test substance in bottles 1, 2, 3 and 4 was determined at the end of the test.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Containing inoculum and medium only.
- Abiotic control: Containing test substance and water.
- Toxicity control: Containing test substance, reference compound, inoculum and medium.
- Other: Procedural control - Containing reference compound, inoculum and medium.
Reference substance:
other: Sodium benzoate
Test performance:
The results showed that the percent recovery of the test substance from test substance + water and from test substance + test medium + inoculum were 114 % and 97 %. It revealed that the recovery method of the test substance used in the study was feasible.
The percentage degradation of reference compound (94.6 %) calculated from the oxygen consumption was not less than 65 % by 14 days.
The percentage degradation of toxicity control (76.3 %) calculated from the oxygen consumption was more than 25 % by 14 days.
Key result
Parameter:
% degradation (O2 consumption)
Value:
35.9
Sampling time:
28 d
Key result
Parameter:
% degradation (test mat. analysis)
Value:
82.1
Sampling time:
28 d
Details on results:
At the end of the test, the percentage primary biodegradation of test suspensions was higher than the BOD percentage biodegradation at the end of the test. Considering of the recovery rates, the reason that the percentage primary biodegradation of test suspensions was higher might be: during the test the structure of the test substance was changed and the parent compound transformed to some intermediate substances which did not degrade further, or degraded slowly, so the consumed DO amount was limited. As the parent substance can not be detected at the end of the test, the residual amount of test substance was low and the percentage primary biodegradation was higher.

Table 3       % biodegradation by BOD

 

Time

(d)

Test Suspension

Reference control

Toxicity control

Bottle 2

Bottle 3

Bottle 4

Mean

1

2.0

1.7

0.6

1.4

55.4

35.2

2

3.8

4.8

2.6

3.7

70.8

51.5

3

5.9

7.6

3.9

5.8

78.9

59.1

4

9.4

12.5

6.5

9.5

84.2

64.7

5

14.5

17.4

11.1

14.3

86.2

66.8

6

15.6

19.4

16.9

17.3

86.2

68.2

7

19.5

20.6

19.1

19.7

88.1

68.4

8

20.8

23.8

20.2

21.6

90.3

69.9

9

22.3

24.8

22.1

23.1

90.3

71.2

10

21.0

22.1

22.2

21.8

90.5

72.5

11

19.6

20.5

20.6

20.2

91.6

73.6

12

17.0

18.4

17.8

17.7

91.9

74.0

13

14.5

16.6

16.2

15.7

92.5

75.0

14

14.8

17.5

17.0

16.4

94.6

76.3

15

16.8

19.7

19.2

18.6

-

-

16

18.2

22.4

21.5

20.7

-

-

17

20.9

24.9

23.1

23.0

-

-

18

24.6

25.6

25.3

25.2

-

-

19

29.2

26.9

28.6

28.2

-

-

20

30.4

30.0

28.9

29.8

-

-

21

31.4

32.2

30.2

31.3

-

-

22

32.7

32.8

31.5

32.3

-

-

23

33.9

32.8

31.5

32.7

-

-

24

34.6

31.6

33.2

33.1

-

-

25

35.5

32.1

37.0

34.9

-

-

26

36.4

32.5

36.3

35.1

-

-

27

36.9

32.4

36.0

35.1

-

-

28

38.1

32.8

36.8

35.9

-

-

 

Table 4       Residual test substance at 28 d and determination of abiotic and primary degradation

 

Bottle

Residual test item

(mg)

Abiotic Degradation

(%)

Primary degradation

(%)

1

12.25

17.2

-

2

3.188

-

74.0

3

2.402

-

80.4

4

0.98

-

92.0

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was considered to be inherently biodegradable under the conditions of this test.
Executive summary:

OECD 302C (2012) - The inherent biodegradability of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was assessed in accordance with OECD Procedure 302C ‘Inherent Biodegradability, Modified MITI Test II’, adopted 12 May 1981.

Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was added to three bottles containing medium and sludge inoculum (5 mg solids/L) to give a nominal test concentration of 32 mg/L. One control culture contained inoculated medium alone was prepared. Two cultures containing inoculated medium plus the reference substance sodium benzoate (100 mg/L) of which one also contained Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid (32 mg/L) in order to assess the potential inhibitory effects of the test substance on the microbial inoculum. A final abiotic control contained Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid and medium only to assess the impact of abiotic degradation on the test item. The test system comprised of an automated system for oxygen (O2) generation and the cultures were stirred and held in a thermostatically-controlled water bath.

 

The reference substance and toxicity controls achieved 94.6 and 76.3 % biodegradation after 14 days of incubation, confirming the validity of the test.

 

The abiotic control achieved 17.3 % degradation by Day 28 indicating the abiotic factors would influence the primary degradation of the test item in the test system.

 

The percent biodegradation of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid, based on O2 consumption / BOD was 35.9 % at Day 28. Recovery of extracted test item residues from the test media at Day 28 indicated that primary biodegradation was 82.1 %.

 

Under the conditions of this test, Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid can be described as being inherently biodegradable (i.e. primary biodegradation was > 70 %).

Description of key information

28 day biodegradation = 25 %, not readily biodegradable; OECD 301F; Dickinson, R. (2012)

28 day primary biodegradation = 82.1 %, inherently biodegradable; OECD 302C; Chenfang, M. (2012)

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, fulfilling specific criteria
Type of water:
other: mixture of sewage, soil and natural water

Additional information

OECD 301F (2012) - The ready biodegradability of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was assessed in accordance with Directive (EC) 440/2008, C.4-D, ‘Determination of Ready Biodegradability, Manometric respirometry’ and OECD Procedure 301F ‘Ready Biodegradability, Manometric Respirometry Test’, adopted 17 July 1992.

 

Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was added to two bottles containing mineral salts medium inoculated with activated sludge (30 mg solids/L) to give a nominal test concentration of 50 mg O2/L. Two control cultures contained inoculated mineral salts medium alone. Two cultures contained inoculated mineral salts medium plus the reference substance sodium benzoate (50 mg O2/L) of which one also contained Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid (50 mg O2/L) in order to assess the potential inhibitory effects of the test substance on the microbial inoculum. The test system comprised of an automated system for oxygen (O2) generation and the cultures were stirred and held in a thermostatically-controlled water bath.

 

The blank-corrected oxygen demanded by the culture containing the reference substance had achieved 15.44 mg O2/500 mL or 62% of the ThOD (25 mg O2/500 mL) after 3 days of incubation.

 

In the presence of Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid, degradation of sodium benzoate had achieved 67 % by Day 3. Cumulative levels of oxygen consumption by the controls after 28 days (14.78 and 11.01 mg O2/500 mL, equivalent to 29.56 and 22.02 mg O2/L) were considered to be acceptable for this assay system. These results confirm that Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was not inhibitory to the activity of the microbial inoculum and that the test was valid.

 

Mean oxygen consumption in mixtures containing Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was equivalent to 10 % of the theoretical value (25 mg O2/500 mL) after approximately 11 days and 25 % at the end of the test (Day 28), therefore, Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was not considered to be readily biodegradable under the conditions of this test.

OECD 302C (2012) - The inherent biodegradability of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was assessed in accordance with OECD Procedure 302C ‘Inherent Biodegradability, Modified MITI Test II’, adopted 12 May 1981.

Tetraesters of pentaerythritol with 2- methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid was added to three bottles containing medium and sludge inoculum (5 mg solids/L) to give a nominal test concentration of 32 mg/L. One control culture contained inoculated medium alone was prepared. Two cultures containing inoculated medium plus the reference substance sodium benzoate (100 mg/L) of which one also contained Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid (32 mg/L) in order to assess the potential inhibitory effects of the test substance on the microbial inoculum. A final abiotic control contained Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid and medium only to assess the impact of abiotic degradation on the test item. The test system comprised of an automated system for oxygen (O2) generation and the cultures were stirred and held in a thermostatically-controlled water bath.

 

The reference substance and toxicity controls achieved 94.6 and 76.3 % biodegradation after 14 days of incubation, confirming the validity of the test.

 

The abiotic control achieved 17.3 % degradation by Day 28 indicating the abiotic factors would influence the primary degradation of the test item in the test system.

 

The percent biodegradation of Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid, based on O2 consumption / BOD was 35.9 % at Day 28. Recovery of extracted test item residues from the test media at Day 28 indicated that primary biodegradation was 82.1 %.

Under the conditions of this test, Tetraesters of pentaerythritol with 2-methylpropanoic acid and 3,5,5-trimethyl-hexanoic acid can be described as being inherently biodegradable (i.e. primary biodegradation was > 70 %).

The results of the OECD 302C are unequivocal, where all guideline validity criteria were satisfied. The test result concluded that biodegradation of the test item was 82.1 %, in excess of the ≥70 % requirement* for establishing an inherently biodegradable substance.

*ECHA, Guidance on Information Requirement and Chemical Safety Assessment, Chapter R.11: PBT/vPvB Assessment, Version 3 (June 2017)